The invention relates to fixed ratio traction roller transmissions with adjustable contact forces applied to the traction surfaces of the transmission.
Traction roller transmissions require relatively large engagement forces between their traction surfaces to prevent slippage. Various means for applying such contact forces are shown in "Mechanical Designs and Systems" Handbook, pages 14-8 and 14-9, McGraw-Hill, New York, 1964. Among other arrangements, there are shown in FIGS. 14.6 and 14.7 planetary-type traction roller transmissions wherein the outer rings are slightly undersized to compress the roller arrangements therein in order to provide the required contact forces. While these arrangements are quite simple, they are capable of providing the same constant traction force independent of the need, that is, independent of the torque transmitted through the transmission, and they provide the same losses no matter whether the full or only a small amount of power is transmitted. There are, however, applications where these characteristics are quite acceptable. A transmission for a small aircraft engine for example would be exposed to a relatively constant load. Cruise load and take-off load do not differ very much and the engine is run only very little under idle load where the losses would be relatively high.
However, such transmissions are difficult to manufacture and to assemble. Heating an undersized ring for assembly may be possible for relatively small transmissions but not for larger transmissions. In any case, such transmissions require the greatest manufacturing accuracies in order to arrive at the desired loading. Besides, slight wear after some time of use reduces the contact forces and this may result in slippage and rapid wear.